Pages

Monday, November 30, 2009

First...Go HERE and see this AWESOME video of Antarctic Starfish [Odontaster validus (99% of the ones in the pic) and some Lysasterias (the big white one) thrown in for good measure] feeding on the dead carcass of a dead seal pup!! Ha! take that mammals! And there's some big Antarctic nemertine worms (probably Parborlasia corrugatus) thrown in for good measure!!

What??? You want MORE time lapse???! Here's some Canadian Atlantic species thrown in for good measure! Looks like primarily Leptasterias polaris (big 6 rayed beast) and Solaster endeca (8-12 armed one with stripes)And to the music of Benny Hill no less!

And yet, EVEN MORE Time Lapse video?? here ya'go! A tiny aquarium asterinid extending its stomach out onto the glass to feed!

Finally, here's some Patiria miniata gliding over the bottom of the Pacific!

If ya' skip over all of the jellies and other non-echinoderm (but still pretty cool) animals, towards the end is a GREAT video of the swimming sea cucumber Enypniastes from the Gulf of Mexico!! (shown above):

There's been a flurry of "best of" type photos, including this cool shot of a bunch of brisingids (Novodinia spp.) and a goniasterid (looks like Evoplosoma) perched on a bunch of deep-sea corals in and around New Zealand (>1000 m based on the original captions).Its a light Echinoblog week but here in the US, its Thanksgiving week, and everything is just a little bit slower! Especially with everything getting colder and darker!

There will continue to be sporadic, light posts this week..with next week back to "normal"...

Tuesday, November 17, 2009

And what animal is more iconic to this area then Pisaster ochraceus (family Asteriidae)-the familiar intertidal Ochre Star found on rocky, mussel-laden substrates on from Alaska to California to Mexico. Some more basic information is here.Interest on this species has shifted over the years and seems to change based on some of the "big science" of the day. Yet another sign of how the humble starfish has incorporated itself into the fabric of the BIG scientific picture!

So, today some highlights of the importance of the ever-humble intertidal Pisaster ochraceus and how its study has varied over the years....

1. The Keystone Species Concept-Ecology's Posterchild. Probably one of the most lasting ideas from the 1960s and 1970s was the hypothesis developed by ecologist Robert T. Paine who identified Pisaster ochraceus as a keystone species (keystone shown below in grey).To quote Wikipedia:

A keystone species is a species that plays a critical role in maintaining the structure of an ecological community and whose impact on the community is greater than would be expected based on its relative abundance or total biomass

This keystone is a crucial block in an arch that keeps it from collapsing. This is analogous for Pisaster's influence on the mussels and the other invertebrates that exist in a rocky intertidal ecosystem. The loss of the "keystone species" results in a drastic shift among these species....The idea has endured and while not embraced by everyone- remains a mainstay in basic ecology books. More details on this notion can be found here.Pisaster along with its prey, the mussel Mytilus are almost ALWAYS the featured example... the POSTER child for the keysone concept-and for this reason, is probably even better known then the Atlantic Asterias!This was (and continues to be) an important ecological notion during a time when the ecosystem and ecologists were in ascendance and ecology was a huge primary mainstay of biological research!2. Pisaster as a Portent of Change??The Canary in the Cage of Climate Change??Probably one of the biggest, new research directions these days?

Understanding Climate Change and in turn...increased ocean temperature, which has a HUGE impact!

It affects ocean water chemistry. Water chemistry in turn can change everything from mineral absorption, feeding behavior, physiological systems to larval settlement. These in turn can have influence on MILLIONS of tiny larvae in the water. As well as the MANY adults those starfish grow into.

This translates into many people interested in the effects of increased temperature and heat relative to the ability of common species to adjust. Will Pisasterochraceus take on a new status as a possible indicator species (i.e., canary in a coal mine) for climate change effects in marine systems?

Here is a survey of three recent studies (2008-2009) that have looked at how Pisaster holds up!

Their paper details how Pisaster ochraceus was observed to increase the amount of colder water in their body cavity lowering their body temperature during the subsequent low tide in response to the temperature.

But climate change has a huge potential impact on animals that do this...to quote in their words:

When placed in a global change context, these results suggest that a continued increase in ocean temperature may compromise the ability of sea stars to avoid thermal stress during aerial exposure at low tide.

Has the humble Pisaster ochraceus gone from ecological poster child to a possible portent of climate change to come??? Time will tell....

But the short version is, that they are remote islands that are protected as a wildlife refuge. The Farallons are great for birdwatching and have lots of great (hopefully still...) pristine intertidal reef habitat.

Plus, as a bunch of rocky islands out on the outskirts of San Francisco Bay, you get lots of this...

Along with many of the classic California invertebrate fauna..

Leptasterias "hexactis", shown here with brooding eggs!! This is part of the Leptasterias species complex which I have written about here and hereand, of course, the good ol' workhorse starfish Pisaster ochraceus, which I will be writing up in the blog later THIS WEEK!!!

and just because they're so dang beautiful...these mollusks too!!! This used to be called Tonicella lineata, but I think the name's been changed recently.......and back in the Paleozoic when I took Intertidal Ecology, this thing was called Calliostoma, but I gots no idea what the kids are calling it these days!GO check out the Rocky Shore Partnership BLOG and I'll be back in a few days with some PISASTEROUS starfishy goodness for all o' y'all!

I have mentioned Tosia before on the blog...It is a starfish in the family Goniasteridae and its genus name is the Latin word for "Inestimable" which alludes, of course, to the animals' incredible natural beauty!

Tosia, as I define it, is found ONLY in Australia, where it is quite abundant and relatively well-known to the people who study marine biology thereabouts. One species in particular, Tosia australis, occurs widely throughout the temperate southern part of Australia.

(Image courtesy of Kate M. Naughton!)

Taxonomists have been noticing T. australis for YEARS and describing a myriad of species. Over the years, some FOURTEEN species have been described-but refinement of species concepts (and removal of unecessarily redundant species) have whittled down the total number to three.

It has led to the identification of what's called the Tosia australis species complex!! That's what happens when you have a lot of closely-related populations that all may or may not be different species.

Something NEW! Brooding Discovered!
So, for an animal that occurs so close to shore, surprisingly little was known about it. In the 90s it was discovered that Tosia australis was a SPECIAL kind of starfish!! It showed an unusual reproductive behavior: BROODING juveniles! That is to say, its offspring live on the adults.
Not too unusual in vertebrates, but VERY unusual in starfish!

Also, Tosia australis has been known since 1840-so it took over 150 years for them to discover that it brooded juveniles!! So, this led to some close observation.

(Image courtesy of Kate M. Naughton!)

So, the investigative talents of Ms. Naughton and Dr. O'Hara were applied towards the question!

Did the difference in larvae mode also translate into further biological differences??

During a museum visit to Melbourne, I was talking shop with Kate and Tim. I was pretty sure that all the morphological variation in the species complex would translate into regional or environmental differentiation VS. Tim who believed that they would split out by larval type.

Larvae in several other species is highly variable but often did not translate into phylogenetic differences..so I figured it would probably do the same here.

And in fact, I was SO confident I was right, that I wagered a gentlemen's bet with Dr. O'Hara that I would be right!

So-I said: "Go get the DNA and prove me wrong!"

And so they did (and had started before I had made the bet!)

Oops! Guess I just lost 10 bucks!
The final analysis following a survey of many specimens from Victoria, Tasmania, and South Australia supported three different species, including something NEW that hadn't been observed before!!!

T. neossia is very similar to the well-known T. australis but, aside from a bunch of external morphological features, one important feature sets them apart....

The difference is in the Larvae (i.e., juvenile starfish)!

One of the fundamental differences here is that of the difference in larvae between Tosia australis and T. neossia!

The new species Tosia neossia had BOTTOM larvae with large yolky eggs (this kind of egg is called lecithotrophic)!!

(Image courtesy of Kate M. Naughton!)

Unlike more "typical" larvae, these tiny guys were negatively buoyant (that is to say, they sink rather then float)!

They are emitted from the mother and crawl along the bottom using little lobes to get around until they fully develop into larval adults. These little BOTTOM larvae (shown here as early stage larvae) can be seen here (courtesy of Kate Naughton!)

(Image courtesy of Kate M. Naughton!)

Here is where the larvae begin to change into what Kate calls the "tripod phase". These utilize a large lobe that helps move the larvae around before it begins to attach someplace on the ground after developing to the right stage....

(Image courtesy of Kate M. Naughton!)

....And finally, here is the settled larvae (oral view-looking up into the mouth). Note the tiny red dots, which will eventually become the eyespots!

This little fellow will develop into what will eventually become

(Image courtesy of Kate M. Naughton!)

....the adult!

This is in direct CONTRAST to Tosia australis which has SWIMMING juveniles that emerge from the aboral surface (via gonopores on the top surface). In contrast to the larval juveniles of T. neossia, T. australis has eggs that are postively buoyant and are covered with small CILIA!! That is, they have little beating hair-like threads that can keep them swimming before they settle out somewhere.

This week: fun ancient etymological mysteries!! Forget the true meaning of Christmas, What is the true meaning of Aristotle's Lantern???

Based on a recent paper (Cahiers de Biologie Marine 49: 299-302) by Eleni Voultsiadou and Chariton Chintiroglou at Aristotle University in Thessaloniki, Greece we have a new perspective on the roots of the special jaw apparatus found in sea urchins (see below).

At face value this seems reasonable enough and enough historians have seemingly verified the story over the years.... (or have they?)

But what if Aristotle did NOT, in fact, mean that the JAW was the "lantern"????

WHAT IF Aristotle's Lantern ACTUALLY referred to the WHOLE BODY (i.e., the test)?? And what we've been taught all along was actually wrong (or mistaken)??

Apparently there had been some historical ambiguities with the original translation. From Aristotle's original History of Animals as such (boldface is mine):

In respect of its beginning and end the mouth (or body) of the urchin is continuous, though in respect of its superficial appearance it is not continuous, but similar to a lantern not having a surrounding skin.

Although several scholars have since embarked upon a historical study of the etymological roots of Aristotle's Lantern (most of whom seemed to be happy with the "lantern" as the translation), no actual archeological evidence had actually been brought to bear on the question.

(An ancient "lamp" p.s. to paleontology students? this is where the phrase "lamp shell" for brachiopod comes from!)

The scholarship of Voultsiadou & Chintiroglou have discovered that ancient Greek lamps (circa 5th to 9th c. BC) (i.e., the light source, usually candle or oil lamp) were placed insidelanterns, which were usually translucent skins or perforated ceramic or bronze, to protect the light source from the wind. Thus preventing them from blowing out.

Thus, an ACTUAL lantern from Aristotle's time, looks like this (remember the lamp or light source goes inside):

(A Vergina lantern from the tomb of King Philip II, dated to the 4th Century BC in Northern Greece)

Now, compare and contrast with the MODERN version of a lantern! (with a "lamp" inside)

(I wish I was kidding about this-but isn't it awesome?)

They proceed to outline how all of the additional incongruities of the original passage can explained based on the assumption that Aristotle was comparing the sea urchin test with a bronze lantern, distinguishing it from those ancient lanterns which were made of skin or other soft material.Thus, they propose that the "test of the sea urchin and NOT the jaw apparatus should be called 'Aristotle's Lantern'."

Monday, November 2, 2009

So, for various reasons, I thought I would do something a little unusual today and actually delver into some basic "how do you tell the difference between x and y" type stuff today. Why? Especially when you can find these sorts of characteristics listed in any Invertebrate Zoology text book?

A confluence of things:

1. Its November. And all over the country, bunches of Invertebrate Zoology students are probably hitting the "Echinodermata" part of their class by now. Let's make it easier for them!

2. Certain high-traffic informational websites, which shall remain nameless,seem to have MIXED UP the difference between asteroids (starfish, sea stars) and ophiuroids (serpent stars, brittle stars, basket stars). And SO, I feel its about the right time to make this information more WIDELY available...

3. I've never done it before!

So, here's some basics!

To start off, BOTH asteroids and ophiuroids are members of the phylum ECHINODERMATA. To show the parallel, humans are members of the phylum CHORDATA. Surprisingly though Chordates and echinoderms are both more closely related to one another then they are to say, insects, mollusks, or crustaceans.

First, Starfish!!

Starfish belong to the Class ASTEROIDEA . When you look at the roots words "Aster" means STAR and "oid" literally means "resembling" or "like"..So scientific term translates to "Star-like".In the truest sense, the 'common name" is ASTEROIDS.

But of course, these are also referred to by a variety of names, so that they are not confused with asteroids in space!:

sea star. starfish. In Spanish: estrella de mar. In French: etoile de mer. In Japan, they are called hitode which alludes to the name for "hand" or "palm".at about Ophiuroi?The given name for ophiuroids is a little more indirect. The class name "Ophiuroidea" refers to "Ophios" which refers to the arms as snake or serpent and "oidea" which means "resemble" or "like"...probably in reference to the arm shape and/or behavior of the animal when alive.

The resemblance to asteroids was noticed early on, of course. And several early designations of these animals actually refer to them as "Asterias" which is the name later tied specifically to asteroids.

So, How do you Tell them APART???

Some easy diagnostic characteristics!

1. The Madreporite or Sieve Plate. You know that offset "hole" that you see on starfish like this one?

This plate is thought to serve as (at least) one place where water enters the internal body cavity of the animal. ALL echinoderms have a madreporite-but its location and shape is modified to one degree or another.

In asteroids the madreporite (also called a sieve plate) is located on the top or aboral surface as indicated by the red circle.BUT in ophiuroids (brittle stars and such) the madreporite is located on the BOTTOM or ORAL surface. As seen here:2. Tube Foot Groove in Asteroids (starfish, sea stars) is OPEN. Although the degree that this groove is open varies, it should always be open to the outside. The tube feet emerge from this open groove and lead into the mouth.In contrast, such a groove is ABSENT in ophiuroids (brittle stars). The oral surface of the arms is covered over with a "ventral" plate. The tube feet can emerge through small openings but they are NOT open to the outside in the way that asteroids are....3. The Fundamental Structure of the arm is DIFFERENT.
In asteroids-there are internal ossicles, which act as sort of support struts. The TUBE FEET emerge through these struts and emerge into the tube foot groove.

Here is a cut away showing these internal ossicles called AMBULACRALS which run down the radius of each arm. These ossicles join and form a sort of rafter-like formation that sit OVER the open tube foot groove (above). So, the tube feet drop down through the ambulacrals and emerge in the tube foot groove.Ophiuroids actually DO have these structures, but they are modified quite differently into solid forms that resemble vertebrae (i.e., the bones in our spine).

In ophiuroids, these vertebrate are tightly enclosed by additional plates that tightly cover over the surface of the arm, including the bottom (see above). Tube feet emerge on the bottom, but only through special pores and NOT through the corresponding ambulacral ossicles.4. The Mouth and associated skeletal parts is different. At this point, I can start to get into a whole bunch of complicated skeletal jargon associated with the skeleton that forms the mouth frame in a starfish (aka an asteroid-seen here looking down through a mouth)....versus the one that forms the mouth of an ophiuroid... (seen here looking at the oral surface up into the mouth). Basically, there's a WHOLE BUNCH of changes in the skeletal architecture surrounding the mouth, as its directed towards a substantially different way of life...

(note that brittle stars don't drop an eversible stomach out of their mouth!)5. The Overall Body structure is different. The arms and disk of a starfish tend to be confluent with one another....Plus, the body cavity between the arm and disk is pretty open.

In brittle stars, the arms and disk are sharply set off from one another. The disk is a distinctly separated structure from the rest of the arms.Asteroids and Ophiuroids are DIFFERENT but closely related.

There are literally, whole books, papers, and multi-year studies written on the subject of which characteristics are used to define the definition of "asteroid" versus "ophiuroid" (often in relation to older fossil forms) and it's important not to call one the other!! (even with common names).In the truest sense, Ophiuroids are not " sea stars" or "starfish".

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
Need to hire an invertebrate zoologist/marine biologist? Please contact me!